The breakthrough comes from using capacitors as batteries. Up until now this has not been feasible because there hasn’t been a strong enough insulator to make this approach compelling. However, EEstor, the company who have made the breakthrough have applied for a patent for a highly insulated capacitor.

In their patent application, it suggests that:

the charge storage is much higher than anything achieved in an academic lab: 52 kilowatt-hours in a 2,000 cubic inch capacitor array. A rough conversion calculation suggests that this is over 10 times the power density of standard lead-acid batteries.

The Ars Technica article goes on to note that:

the Associated Press is reporting that the ZENN Motor Company, which makes compact electric cars, plans to start using the capacitors before the year is out. The company has invested in EEStar in return for production goals being met and so is in a position to know how realistic its claims are

If this has any basis in fact, it could have incredible consequences for the reduction of carbon emissions from transport and from the environment in general with the reduction in the use of the particularly nasty chemicals which currently go to make up batteries.